Concept

A ratio is a comparison of two quantities. 
A fraction is a number that names part of a whole or part of a group. The denominator represents the total number of equal parts the whole is divided into.

Rule

• The order of the values in a ratio relates directly to the order of the quantities described.
• When you are describing a part of a whole, a fraction is appropriate.
• When you are comparing two numbers, a ratio is appropriate.
• The most common way to write a ratio is as a fraction, 36.
• Ratios can also be written using the word "to," as "3 to 6", or by 
• using a colon between the two numbers, 3:6.

Example

25of the cars in the parking lot are blue, and the rest are yellow.

What is the ratio of yellow cars to blue cars in the parking lot?

Solution

1. The numerator of the fraction (2) tells how many blue cars are in the parking lot. The denominator of the fraction (5) represents the total number of yellow and blue cars in the parking lot. 
   To find how many yellow cars are in the parking lot, subtract the numerator (2) from the denominator (5).  5 - 2 = 3
   There are 3 yellow cars in the parking lot.
2. The order of the values in a ratio relates directly to the order of the quantities described. The ratio needed is yellow cars to blue cars. The number of yellow cars (3) needs to go first when writing the ratio.
   There are 3 yellow cars to 2 blue cars.
   Write the ratio: 
   3:2

Pre-requisite Skills

Understand Ratios (6.6.1)

Fractions - Part of a Whole (4.14.1)